const numArr: (number | string)[] = [1, "2", 3];
const stringArr: string[] = ["a", "b"];
const undefindArr: undefined[] = [undefined];

type User = {
  name: string;
  age: number;
};
class Teacher {
  name: string;
  age: number;
}
const objectArr: User[] = [
  new Teacher(),
  {
    name: "dell",
    age: 28
  }
];

// 元组tuple
const teacherInfo: [string, string, number] = ["dell", "male", 18];
const teacherList: ([string, string, number])[] = [["dell", "male", 18]];
